The present invention relates to the liquefaction of coal to produce a normally liquid product which is low in sulfur and nitrogen and has a high API gravity. The invention also relates to the upgrading of coal/heavy petroleum oil slurries to provide low sulfur, low nitrogen products.
As a consequence of the increasing cost and diminishing supplies of petroleum, much research is being conducted into better ways of obtaining synthetic fuels from solids such as coal and from heavy petroleum oils. Furthermore, as a consequence of increased emphasis on the reduction of air pollution, fuels with low sulfur and low nitrogen contents are in great demand. Unfortunately, however, most coals and heavy oils contain large amounts of sulfur and nitrogen which necessitate additional costly sulfur and nitrogen removal steps, further increasing the cost of fuels derived from these sources.
In many processes for coal liquefaction hydrogen is supplied by a liquid donor solvent. In such processes the function of any catalyst is to rehydrogenate the solvent by adding molecular hydrogen to it; thus, the solvent acts as a medium to carry hydrogen from the catalyst to the solid coal. Numerous problems in prior art processes resulted from the presence of insoluble solids in the liquid product. Typically, the liquid product from a coal liquefaction process has a high molecular weight which makes it very difficult to separate fine insoluble solids, e.g., coal residue. It has generally been taught that these insoluble solids must be separated prior to further processing in order to prevent downstream catalyst deactivation.
Typical of the prior art processes is the Gulf catalytic coal liquefaction process disclosed in Coal Conversion Technology, Smith et al, Noyes Data Corporation, 1976, where a slurry of coal and process-derived solvent is forced up through a bed of catalyst at 900.degree. F. and 2000 psig. The product, as taught in Sun W. Chung, National Science Foundation, Ohio State University Workshop, "Materials Problems and Research", Apr. 16, 1974, has a gravity of 1.2.degree. API, a sulfur content of 0.11 weight percent and a nitrogen content of 0.63 weight percent.
Another typical and well known prior art process is the Synthoil process wherein a coal solvent slurry is pumped into a catalytic fixed bed reactor with hydrogen at a high velocity. Similarly to the above Gulf process, the Synthoil process also produces a liquid product, as taught in "Coal Liquefaction", Sam Friedman et al, presented at NPRA National Fuel and Lubricants meeting, November 6-8, 1974, Houston, Texas, which products have a gravity of -0.72.degree. API and a sulfur content of 0.2 weight percent.